The present invention relates generally to a semiconductor device and, more particularly, to a batch processed, semiconductor device including an electrical transducer.
The need for highly sensitive, miniature-sized pressure sensors is important for incorporation into micro-electromechanical systems (MEMS) devices. Pressure sensors of this type have many applications, including uses in motor vehicles. One motor vehicle application requires the use of pressure sensors for measuring both ambient and subatmospheric pressure levels. In internal combustion engine applications, fine control of fuel metering has required that the rapidly-fluctuating pressure levels within the intake manifold of the engine be measured as well as the less-rapidly fluctuating ambient pressure levels. Sensors able to measure these pressures reliably and with adequate response time have been difficult to obtain and are typically expensive.
A majority of the currently employed pressure sensors are piezoresistive devices, well known to those skilled in the art. However, capacitive pressure sensor devices are becoming increasingly more of the focus in the industry because of their higher pressure sensitivity, lower temperature sensitivity, and reduced power consumption. Because piezoresistive devices can be more cheaply produced and are currently more reliable, they remain, however, the more popular of the known pressure sensors. Research continues on the capacitive pressure sensor devices to reduce their cost of manufacture and increase their reliability because of their inherent advantages.
Many variations of capacitive pressure sensors are known in the art. Capacitive pressure sensors typically measure pressure by the capacitive changes resulting from variations in the distance between a movable diaphragm and a substrate that occur because of pressure changes. A vacuum sealed chamber is defined in the sensor, where an internal electrode is formed on the substrate within the chamber and a second electrode is formed as part of the movable diaphragm. As the pressure outside of the chamber increases or decreases, the diaphragm moves towards or away from the substrate, and the charge on the electrodes changes giving an indication of the pressure change.
These sensors are affected by parasitics and external interference since the signal is amplified a significant distance from the transducer. What is needed is a monolithic fully-integrated pressure sensor that is cost-effective, reliable and robust, and includes an electrical circuit with the transducer. It is therefore an objective of the present invention to provide such a sensor.
In accordance with the teachings of the present invention, a semiconductor device is disclosed that includes a transducer and electrical circuit within a vacuum sealed chamber. This invention is related to some of the concepts described in U.S. Pat. No. 5,929,497, which is assigned to the assignee of the present invention and expressly incorporated herein by reference and as described in the paper, xe2x80x9cA Monolithic Fully-Integrated Vacuum-Sealed CMOS Pressure Sensorxe2x80x9d, which is authored by the inventors of the present invention and expressly incorporated herein by reference, and which at the time of filing the subject application has not been published or otherwise publicly disclosed. This invention can be used in many applications including, for example, precision altitude measurements and microweatherstations.
The development of integrated pressure sensors containing on-chip circuitry has become a primary focus of MEMS research in order to achieve improved performance, cost reduction and realization of the system-on-chip concept for capacitive pressure sensors. Such sensors reduce the effects of parasitics and external interference because the signal is amplified in close proximity of the transducer, however, they also pose interesting challenges in merging transducer and circuit processes, maintaining testability, and achieving reliable vacuum encapsulation. Vacuum encapsulation is required in many devices to eliminate problems relating to temperature effects of gas expansion, squeeze film damping effects which limit bandwidth and problems relating to stiction during final release of the device. In addition the availability of an assembly ready device can significantly reduce packaging costs associated with hermnetic sealing requirements and permit low cost packaging to be used. The die area required for a sensor having embedded readout circuitry is typically smaller than two separate dies as used in hybrid integration, and any reliability problems associated with inter-chip interconnects are eliminated.
Any yield model for integrate d sensors containing on-chip circuitry is highly process dependent. In the past decade, process equipment has become highly automated thereby providing improved control for processes having high numbers of masking steps. The impact of this improvement in process control is seen in the success of deep-submicron process technology, which has many more masking steps than standard 1 xcexcm CMOS and yet achieves high yield. Thus, the prospect of fabricating sensors using higher mask counts to achieve high performance while obtaining high yield is promising. Other types of semiconductor devices, such as accelerometers, gyroscopes, resonators, etc., also benefit from such on-chip circuit integration technology.
The present invention involves an integrated multi-transducer capacitive barometric pressure sensor that is vacuum-sealed at the wafer level. The interface circuitry is integrated directly with the sealed reference cavity, making the device imnmune to parasitic environmental effects. The overall device process merges BiCMOS circuitry with a dissolved-wafer transducer process, is compatible with bulk- and surface-micromachining, and employs chemical-mechanical polishing (CMP), anodic bonding, and hermetic lead transfers. The sensor achieves 15b resolution and is compatible with low cost packaging. The device includes a programmable switched-capacitor readout circuit, five segmented-range pressure transducers, and a reference capacitor, all integrated on a 7.5xc3x976.5 mm2 die using 3 xcexcm features.
The present invention provides a semiconductor device including a substrate, a first semiconductor region including a recessed area defining a first cavity between the substrate and the first semiconductor region, an electrical transducer positioned within the first cavity, a second semiconductor region including a recessed area defining a second cavity between the substrate and the second semiconductor region, an electrical circuit positioned within the second cavity, and at least one electrode connecting the electrical transducer and the electrical device.
The present invention further provides a semiconductor device including a substrate, a first semiconductor region including a plurality of recessed areas defining a plurality of transducer cavities between the substrate and the first semiconductor region, an electrical transducer positioned within each the transducer cavity, a second semiconductor region including a recessed area defining a circuit cavity between the substrate and the second semiconductor region, an electrical circuit positioned within the circuit cavity, and a plurality of electrodes connecting the electrical transducers to the electrical device.
The present invention yet provides a semiconductor device including a substrate, a first semiconductor region including a recessed area defining a first cavity between the substrate and the first semiconductor region, an electrical transducer positioned within the first cavity, a second semiconductor region including a recessed area defining a second cavity between the substrate and the second semiconductor region, an electrical circuit positioned within the second cavity, at least one electrode connecting the electrical transducer and the electrical device, and a sealing layer extending around the perimeter of the cavities and vacuum sealing the semiconductor regions to the substrate.